This invention relates to thermocouples and more particularly to an economical thermocouple which, based on its low cost, can be employed as a disposable unit.
The prior art is replete with a host of patents and devices describing thermocouple devices of various configurations and constructions.
Essentially, a thermocouple is an electric circuit consisting of a pair of wires of different metals jointed together at one end called the sensing junction and terminated at the other end in such a manner that the terminals are both at the same and a known temperature. This is called the reference junction and the known temperature is called the reference temperature. The terminal leads of the reference junction are connected to a high input impedance amplifier and due to the thermoelectric effect (Seebeck effect) a voltage is created across the reference junction whenever the sensing junction and the reference junction are at different temperatures. The magnitude of the voltage is an indication of the temperature difference. Usually, the reference junction is held at a known constant temperature or is electrically compensated for variations from a preselected temperature.
The prior art has employed a host of different metal wires to implement the thermocouple structure. The materials employed have been Chromel, Alumel, Constanton, copper, iron, platinum, alloys of platinum as platinum and rhodium, tungsten, tungsten-rhenium alloys, nickel and ferrous nickel alloys.
The thermoelectrical emf which causes current flow through a circuit is also dependent upon the junction wire materials and the temperature difference between the junctions. Their characteristics are well known in the field. See a text entitled Electronics Engineers Handbook by D. G. Fink and A. A. McKenzie (1975) (1st Edition) McGraw-Hill, Inc. Section 10, "Transducers".
As indicated, the use of the thermocouple to measure temperature is well known and the applications are many.
In any event, a major problem exists in the measurement of human body temperature. Essentially, each year about 1 billion temperature measurements are made at hospitals in the U.S.A., and the number of measurements made throughout the world is of a greater magnitude. Due to the progress made in the field of medical electronics, there has been a widespread use of the electronic thermometer, especially for hospital use. These devices employ a temperature probe which is coupled to a suitable electronic circuit and display to measure body temperature. The probe is inserted into the mouth of a user during measurement and a display indicates the temperature.
Examples of such instruments are many and many different companies supply and sell such devices for hospital use. It is, of course, apparent that in order to employ such a thermometer for hospital use, one must provide probe isolation from one patient to another. In this manner a plastic sterilized probe cover is employed. The cover is used to enclose the probe for each temperature measurement and is then discarded and a new cover inserted for the next measurement. Even though the covers are disposable and made from an inexpensive plastic, their cost is significant when one considers the number of temperature measurements made during a prolonged interval.
Based upon such considerations, if a savings in this component of only a fraction of a penny or more could be had, this would result in a substantial savings over the course of a year.
Apart from this factor is the fact that the probe section of the thermometer which is constantly being covered and measured is subjected to extensive wear and this probe has to be replaced at frequent intervals as well. The probe is a relatively expensive component in such devices and replacement of the same necessitates a recalibration of the instrument.
A further problem with the conventional thermometer is the excessive time required to take a patient's temperature. Due to the above considerations the plastic covered probe is of a relatively large mass and hence takes an appreciable amount of time to indicate the temperature. In such devices, one must be sure that the displayed temperature is correct and hence one must wait for the plastic covered probe to heat up during a temperature measurement. Any reduction in this time results in a great savings in time due to the huge number of temperature measurements made as described above.
It is therefore an object of the present invention to provide a thermocouple device which, based on its construction, is extremely inexpensive and adapted to replace the conventional probe and plastic cover for human body temperature measurements.
It is a further object to provide a method of manufacturing a thermocouple device which method enables one to provide a rugged low-cost unit particularly adapted for human measurements which unit can provide a rapid response to body temperature.
A further object of the present invention is to provide a method of fabricating a thermocouple employed in measuring temperature.